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Instead of burying them in phones, Japanese mobile carrier NTT DoCoMo wants people to start wearing their SIM cards.

It has developed a SIM card that can wirelessly connect smartphones and tablets to networks and the Internet simply by waving one's hand. The card can also transmit a user's number and other info, separating connectivity from mobile devices themselves.

Unveiled Tuesday, DoCoMo announced a pocket-sized prototype of the technology that it's calling Portable SIM. Subscriber identities can be instantly transmitted to mobile devices with the prototype. That means users don't have to physically insert SIM cards into phones as they do now.

Aside from linking to phones or tablets via Bluetooth and NFC, the SIM contains a user's phone number, usernames and passwords. DoCoMo said it's the world's first SIM-based authentication device that can provide wireless network access.

The prototype, currently 8 cm long, 4 cm wide and weighing 20 grams, will be shrunk so it can fit into a bracelet-style wearable computer, DoCoMo said. Earlier this year, the carrier announced a health-monitoring wristband and smart clothing.

In a series of demonstrations at DoCoMo headquarters in Tokyo, a staffer held the prototype Portable SIM near a SIM-less phone. By linking the two through an app, the phone could receive a call to the number registered on the Portable SIM.

The process, which took a few seconds, was then repeated with a different SIM-less phone.

In another demo, the Portable SIM was used to link different phone numbers to the same phone -- first a number for personal use, and then one for business. The idea is that the same smartphone could be used with different phone numbers in the SIM depending on the time of day, and each number would also trigger certain apps or other custom settings.

"We were considering what comes next after the smartphone and we zeroed in on what functions were essential to customers," Akira Shibutani, manager of the Advanced Technology Group at DoCoMo's Communication Device Development Department, said in a briefing on the device. "We felt that this boiled down to authentication."

The SIM might also be used to connect to other devices too, including PCs, in-car information systems, public phones or bathroom scales. Travelers, for instance, could leave their smartphone at home but get online by waving their Portable SIM in front of a hotel TV, he said.

"When people use multiple smartphones and tablets, this Portable SIM will be a very convenient way to allow you to link to all of them," Kazuaki Terunuma, managing director of the department, said during the briefing.

DoCoMo, Japan's dominant mobile carrier, has applied for Japanese and overseas patents related to the Portable SIM. It's still in the research phase and is not yet compatible with smartphones or tablets on the market.

The company has not decided when the device might be launched in Japan. Overseas sales are a possibility, but this sort of device would be have to be discussed at international standards forums, DoCoMo officials said.

DoCoMo will show off the Portable SIM prototype at Mobile Asia Expo, which kicks off Wednesday in Shanghai.